The Moving Picture Experts Group (MPEG) created the ISO/IEC international Standards 11172 and 13818 (generally referred to as MPEG-1 and MPEG-2 format respectively) to establish a standard for coding/decoding strategies. Although these MPEG standards specify a general coding methodology and syntax for generating an MPEG compliant bitstream, many variations are permitted to accommodate a plurality of different applications and services such as desktop video publishing, video conferencing, digital storage media and television broadcast. A related video encoding standard is the "Draft ITU-T Recommendation H.263: Video Coding for Low Bitrate Communication" (December 1995), which has been promulgated by the International Telecommunications Union. The above standards are herein incorporated by reference in their respective entireties.
In the production and post-production of television and other video material, extreme care is taken to preserve color fidelity, especially to preserve accurate flesh tones. This includes special circuitry in studio cameras, and often special "hand tuning" by a colorist. With such a degree of care taken, it must be noted that the final compression encoding of such material is usually performed by a compression encoder "black box" in which, typically, bit allocation is performed based on a measure of "busy-ness" or texture detail information in each block of the image. That is, the compression encoder allocates more bits to areas of the picture that have more detail information. Since detail information is primarily included within the luminance portion of a television or video signal, scene detail analysis of such a signal is performed using the luminance portion of the television or video signal.
Unfortunately, compression encoders implementing luminance signal detail analysis tend to exhibit, e.g., flesh-tone related artifacts when portions of a television or video signal comprising flesh tones are not associated with a sufficiently "busy" luminance portion. That is, a picture may include a relatively "busy" portion, such that the "busy" portion is allocated an increased number of bits. The picture may also include a relatively non-busy portion that comprises flesh tone colors and other color or content information deemed to be perceptually important (such as advertising logo colors, professional graphics renderings and the like). These important chrominance portions are disadvantageously allocated a decreased number of bits to compensate for the increase in bit allocation to the "busy" portion of the picture. Thus, flesh-tone and other important chrominance aspects of a picture may be inaccurately displayed if within an area of the picture including low luminance detail.
Therefore, a need exists in the art for a high quality encoding apparatus and method that eliminates the above-described artifacts by performing a detail analysis that considers flesh-tone and/or other high value chrominance information.